This invention relates to radiation detection devices for electromagnetic radiation, and particularly to such devices which are useful for a broad band of frequencies and generally isotropic.
On application of this invention is as a radiation hazard meter. The increasing use of high power radio frequency and microwave power sources in military, commercial and consumer applications has resulted in a corresponding increase in concern regarding the potential biological hazards of human exposure to electromagnetic radiation. Although there is some disagreement as to the threshold radiation level which causes serious physiological damage, most medical and bio-engineering researchers agree that this level is far below that which can be sensed by exposed human beings.
For many years, researchers and military and industrial safety personnel have employed several types of instruments for measuring radiation intensity levels in terms of milliwatts per square centimeter. Generally, these instruments are basically r-f power sensing devices with some form of antenna pick-up to intercept the electromagnetic field; see, for example, U.S. Pat. Nos. 1,923,916 and 3,641,439. This instrument type suffers from one or more of several disadvantages. Realizable antennas place limitations on bandwidth, particularly in the lower frequency ranges and do not provide a constant "effective aperture." One instrument employs seven antennas to circumvent this problem. In addition, antennas employ conducting surfaces which, because of interaction effects, degrade the reliability of near field measurements. Since it is to be anticipated that people will be increasingly exposed to radiation fields of many frequencies, a broadband instrument is desirable which is practical in size. Moreover, the instrument should be generally effective without limitation on its orientation to the polarized radiation field.
The monitoring of r-f radiation by resistive sensors, instead of antennas, is described in U.S. Pat. No. 2,496,879 and in the paper, "Thin-Film Spherical Bolometer for Measurement of Hazardous Field Intensities from 400 MH.sub.z to 40 GH.sub.z " by Fletcher and Woods, published in "Non-ionizing Radiation," Sept. 1969, which cites a British Patent 965,559/64 to Woods. The use of thermocouples in waveguides for measuring radiation at radio frequencies is described in U.S. Pat. Nos. 3,384,819, 3,147,436 and 2,106,768.